/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package javax.servlet.jsp;

import javax.servlet.*;
import javax.servlet.http.HttpSession;
import javax.servlet.jsp.tagext.BodyContent;
import java.io.IOException;

/**
 * <p>
 * PageContext extends JspContext to provide useful context information for
 * when JSP technology is used in a Servlet environment.
 * <p>
 * A PageContext instance provides access to all the namespaces associated
 * with a JSP page, provides access to several page attributes, as well as
 * a layer above the implementation details.  Implicit objects are added
 * to the pageContext automatically.
 * <p>
 * <p> The <code> PageContext </code> class is an abstract class, designed to be
 * extended to provide implementation dependent implementations thereof, by
 * conformant JSP engine runtime environments. A PageContext instance is
 * obtained by a JSP implementation class by calling the
 * JspFactory.getPageContext() method, and is released by calling
 * JspFactory.releasePageContext().
 * <p>
 * <p> An example of how PageContext, JspFactory, and other classes can be
 * used  within a JSP Page Implementation object is given elsewhere.
 * <p>
 * <p>
 * The PageContext provides a number of facilities to the page/component
 * author and page implementor, including:
 * <ul>
 * <li>a single API to manage the various scoped namespaces
 * <li>a number of convenience API's to access various public objects
 * <li>a mechanism to obtain the JspWriter for output
 * <li>a mechanism to manage session usage by the page
 * <li>a mechanism to expose page directive attributes to the scripting
 * environment
 * <li>mechanisms to forward or include the current request to other active
 * components in the application
 * <li>a mechanism to handle errorpage exception processing
 * </ul>
 * <p>
 * <p><B>Methods Intended for Container Generated Code</B>
 * <p>Some methods are intended to be used by the code generated by the
 * container, not by code written by JSP page authors, or JSP tag library
 * authors.
 * <p>The methods supporting <B>lifecycle</B> are <code>initialize()</code>
 * and <code>release()</code>
 * <p>
 * <p>
 * The following methods enable the <B>management of nested</B> JspWriter
 * streams to implement Tag Extensions: <code>pushBody()</code>
 * <p>
 * <p><B>Methods Intended for JSP authors</B>
 * <p>
 * The following methods provide <B>convenient access</B> to implicit objects:
 * <code>getException()</code>,  <code>getPage()</code>
 * <code>getRequest()</code>,  <code>getResponse()</code>,
 * <code>getSession()</code>,  <code>getServletConfig()</code>
 * and <code>getServletContext()</code>.
 * <p>
 * <p>
 * The following methods provide support for <B>forwarding, inclusion
 * and error handling</B>:
 * <code>forward()</code>,  <code>include()</code>,
 * and  <code>handlePageException()</code>.
 */

public abstract class PageContext
		extends JspContext {

	/**
	 * Page scope: (this is the default) the named reference remains available
	 * in this PageContext until the return from the current Servlet.service()
	 * invocation.
	 */

	public static final int PAGE_SCOPE = 1;
	/**
	 * Request scope: the named reference remains available from the
	 * ServletRequest associated with the Servlet until the current request
	 * is completed.
	 */

	public static final int REQUEST_SCOPE = 2;
	/**
	 * Session scope (only valid if this page participates in a session):
	 * the named reference remains available from the HttpSession (if any)
	 * associated with the Servlet until the HttpSession is invalidated.
	 */

	public static final int SESSION_SCOPE = 3;
	/**
	 * Application scope: named reference remains available in the
	 * ServletContext until it is reclaimed.
	 */

	public static final int APPLICATION_SCOPE = 4;
	/**
	 * Name used to store the Servlet in this PageContext's nametables.
	 */

	public static final String PAGE = "javax.servlet.jsp.jspPage";
	/**
	 * Name used to store this PageContext in it's own name table.
	 */

	public static final String PAGECONTEXT = "javax.servlet.jsp.jspPageContext";
	/**
	 * Name used to store ServletRequest in PageContext name table.
	 */

	public static final String REQUEST = "javax.servlet.jsp.jspRequest";
	/**
	 * Name used to store ServletResponse in PageContext name table.
	 */

	public static final String RESPONSE = "javax.servlet.jsp.jspResponse";
	/**
	 * Name used to store ServletConfig in PageContext name table.
	 */

	public static final String CONFIG = "javax.servlet.jsp.jspConfig";
	/**
	 * Name used to store HttpSession in PageContext name table.
	 */

	public static final String SESSION = "javax.servlet.jsp.jspSession";
	/**
	 * Name used to store current JspWriter in PageContext name table.
	 */

	public static final String OUT = "javax.servlet.jsp.jspOut";
	/**
	 * Name used to store ServletContext in PageContext name table.
	 */

	public static final String APPLICATION = "javax.servlet.jsp.jspApplication";
	/**
	 * Name used to store uncaught exception in ServletRequest attribute
	 * list and PageContext name table.
	 */

	public static final String EXCEPTION = "javax.servlet.jsp.jspException";

	/**
	 * Sole constructor. (For invocation by subclass constructors,
	 * typically implicit.)
	 */
	public PageContext() {
		// NOOP by default
	}

	/**
	 * <p>
	 * The initialize method is called to initialize an uninitialized PageContext
	 * so that it may be used by a JSP Implementation class to service an
	 * incoming request and response within it's _jspService() method.
	 * <p>
	 * <p>
	 * This method is typically called from JspFactory.getPageContext() in
	 * order to initialize state.
	 * <p>
	 * <p>
	 * This method is required to create an initial JspWriter, and associate
	 * the "out" name in page scope with this newly created object.
	 * <p>
	 * <p>
	 * This method should not be used by page  or tag library authors.
	 *
	 * @param servlet      The Servlet that is associated with this PageContext
	 * @param request      The currently pending request for this Servlet
	 * @param response     The currently pending response for this Servlet
	 * @param errorPageURL The value of the errorpage attribute from the page
	 *                     directive or null
	 * @param needsSession The value of the session attribute from the
	 *                     page directive
	 * @param bufferSize   The value of the buffer attribute from the page
	 *                     directive
	 * @param autoFlush    The value of the autoflush attribute from the page
	 *                     directive
	 * @throws IOException              during creation of JspWriter
	 * @throws IllegalStateException    if out not correctly initialized
	 * @throws IllegalArgumentException If one of the given parameters
	 *                                  is invalid
	 */

	public abstract void initialize(Servlet servlet, ServletRequest request,
	                                ServletResponse response, String errorPageURL, boolean needsSession,
	                                int bufferSize, boolean autoFlush)
			throws IOException, IllegalStateException, IllegalArgumentException;

	/**
	 * <p>
	 * This method shall "reset" the internal state of a PageContext, releasing
	 * all internal references, and preparing the PageContext for potential
	 * reuse by a later invocation of initialize(). This method is typically
	 * called from JspFactory.releasePageContext().
	 * <p>
	 * <p>
	 * Subclasses shall envelope this method.
	 * <p>
	 * <p>
	 * This method should not be used by page  or tag library authors.
	 */

	public abstract void release();

	/**
	 * The current value of the session object (an HttpSession).
	 *
	 * @return the HttpSession for this PageContext or null
	 */

	public abstract HttpSession getSession();

	/**
	 * The current value of the page object (In a Servlet environment,
	 * this is an instance of javax.servlet.Servlet).
	 *
	 * @return the Page implementation class instance associated
	 * with this PageContext
	 */

	public abstract Object getPage();

	/**
	 * The current value of the request object (a ServletRequest).
	 *
	 * @return The ServletRequest for this PageContext
	 */

	public abstract ServletRequest getRequest();

	/**
	 * The current value of the response object (a ServletResponse).
	 *
	 * @return the ServletResponse for this PageContext
	 */

	public abstract ServletResponse getResponse();

	/**
	 * The current value of the exception object (an Exception).
	 *
	 * @return any exception passed to this as an errorpage
	 */

	public abstract Exception getException();

	/**
	 * The ServletConfig instance.
	 *
	 * @return the ServletConfig for this PageContext
	 */

	public abstract ServletConfig getServletConfig();

	/**
	 * The ServletContext instance.
	 *
	 * @return the ServletContext for this PageContext
	 */

	public abstract ServletContext getServletContext();

	/**
	 * <p>
	 * This method is used to re-direct, or "forward" the current
	 * ServletRequest and ServletResponse to another active component in
	 * the application.
	 * </p>
	 * <p>
	 * If the <I> relativeUrlPath </I> begins with a "/" then the URL specified
	 * is calculated relative to the DOCROOT of the <code> ServletContext </code>
	 * for this JSP. If the path does not begin with a "/" then the URL
	 * specified is calculated relative to the URL of the request that was
	 * mapped to the calling JSP.
	 * </p>
	 * <p>
	 * It is only valid to call this method from a <code> Thread </code>
	 * executing within a <code> _jspService(...) </code> method of a JSP.
	 * </p>
	 * <p>
	 * Once this method has been called successfully, it is illegal for the
	 * calling <code> Thread </code> to attempt to modify the <code>
	 * ServletResponse </code> object.  Any such attempt to do so, shall result
	 * in undefined behavior. Typically, callers immediately return from
	 * <code> _jspService(...) </code> after calling this method.
	 * </p>
	 *
	 * @param relativeUrlPath specifies the relative URL path to the target
	 *                        resource as described above
	 * @throws IllegalStateException if <code> ServletResponse </code> is not
	 *                               in a state where a forward can be performed
	 * @throws ServletException      if the page that was forwarded to throws
	 *                               a ServletException
	 * @throws IOException           if an I/O error occurred while forwarding
	 */

	public abstract void forward(String relativeUrlPath)
			throws ServletException, IOException;

	/**
	 * <p>
	 * Causes the resource specified to be processed as part of the current
	 * ServletRequest and ServletResponse being processed by the calling Thread.
	 * The output of the target resources processing of the request is written
	 * directly to the ServletResponse output stream.
	 * </p>
	 * <p>
	 * The current JspWriter "out" for this JSP is flushed as a side-effect
	 * of this call, prior to processing the include.
	 * </p>
	 * <p>
	 * If the <I> relativeUrlPath </I> begins with a "/" then the URL specified
	 * is calculated relative to the DOCROOT of the <code>ServletContext</code>
	 * for this JSP. If the path does not begin with a "/" then the URL
	 * specified is calculated relative to the URL of the request that was
	 * mapped to the calling JSP.
	 * </p>
	 * <p>
	 * It is only valid to call this method from a <code> Thread </code>
	 * executing within a <code> _jspService(...) </code> method of a JSP.
	 * </p>
	 *
	 * @param relativeUrlPath specifies the relative URL path to the target
	 *                        resource to be included
	 * @throws ServletException if the page that was forwarded to throws
	 *                          a ServletException
	 * @throws IOException      if an I/O error occurred while forwarding
	 */
	public abstract void include(String relativeUrlPath)
			throws ServletException, IOException;

	/**
	 * <p>
	 * Causes the resource specified to be processed as part of the current
	 * ServletRequest and ServletResponse being processed by the calling Thread.
	 * The output of the target resources processing of the request is written
	 * directly to the current JspWriter returned by a call to getOut().
	 * </p>
	 * <p>
	 * If flush is true, The current JspWriter "out" for this JSP
	 * is flushed as a side-effect of this call, prior to processing
	 * the include.  Otherwise, the JspWriter "out" is not flushed.
	 * </p>
	 * <p>
	 * If the <i>relativeUrlPath</i> begins with a "/" then the URL specified
	 * is calculated relative to the DOCROOT of the <code>ServletContext</code>
	 * for this JSP. If the path does not begin with a "/" then the URL
	 * specified is calculated relative to the URL of the request that was
	 * mapped to the calling JSP.
	 * </p>
	 * <p>
	 * It is only valid to call this method from a <code> Thread </code>
	 * executing within a <code> _jspService(...) </code> method of a JSP.
	 * </p>
	 *
	 * @param relativeUrlPath specifies the relative URL path to the
	 *                        target resource to be included
	 * @param flush           True if the JspWriter is to be flushed before the include,
	 *                        or false if not.
	 * @throws ServletException if the page that was forwarded to throws
	 *                          a ServletException
	 * @throws IOException      if an I/O error occurred while forwarding
	 * @since 2.0
	 */
	public abstract void include(String relativeUrlPath, boolean flush)
			throws ServletException, IOException;

	/**
	 * <p>
	 * This method is intended to process an unhandled 'page' level
	 * exception by forwarding the exception to the specified
	 * error page for this JSP.  If forwarding is not possible (for
	 * example because the response has already been committed), an
	 * implementation dependent mechanism should be used to invoke
	 * the error page (e.g. "including" the error page instead).
	 * <p>
	 * <p>
	 * If no error page is defined in the page, the exception should
	 * be rethrown so that the standard servlet error handling
	 * takes over.
	 * <p>
	 * <p>
	 * A JSP implementation class shall typically clean up any local state
	 * prior to invoking this and will return immediately thereafter. It is
	 * illegal to generate any output to the client, or to modify any
	 * ServletResponse state after invoking this call.
	 * <p>
	 * <p>
	 * This method is kept for backwards compatibility reasons.  Newly
	 * generated code should use PageContext.handlePageException(Throwable).
	 *
	 * @param e the exception to be handled
	 * @throws ServletException     if an error occurs while invoking the error page
	 * @throws IOException          if an I/O error occurred while invoking the error
	 *                              page
	 * @throws NullPointerException if the exception is null
	 * @see #handlePageException(Throwable)
	 */

	public abstract void handlePageException(Exception e)
			throws ServletException, IOException;

	/**
	 * <p>
	 * This method is intended to process an unhandled 'page' level
	 * exception by forwarding the exception to the specified
	 * error page for this JSP.  If forwarding is not possible (for
	 * example because the response has already been committed), an
	 * implementation dependent mechanism should be used to invoke
	 * the error page (e.g. "including" the error page instead).
	 * <p>
	 * <p>
	 * If no error page is defined in the page, the exception should
	 * be rethrown so that the standard servlet error handling
	 * takes over.
	 * <p>
	 * <p>
	 * This method is intended to process an unhandled "page" level exception
	 * by redirecting the exception to either the specified error page for this
	 * JSP, or if none was specified, to perform some implementation dependent
	 * action.
	 * <p>
	 * <p>
	 * A JSP implementation class shall typically clean up any local state
	 * prior to invoking this and will return immediately thereafter. It is
	 * illegal to generate any output to the client, or to modify any
	 * ServletResponse state after invoking this call.
	 *
	 * @param t the throwable to be handled
	 * @throws ServletException     if an error occurs while invoking the error page
	 * @throws IOException          if an I/O error occurred while invoking the error
	 *                              page
	 * @throws NullPointerException if the exception is null
	 * @see #handlePageException(Exception)
	 */

	public abstract void handlePageException(Throwable t)
			throws ServletException, IOException;

	/**
	 * Return a new BodyContent object, save the current "out" JspWriter,
	 * and update the value of the "out" attribute in the page scope
	 * attribute namespace of the PageContext.
	 *
	 * @return the new BodyContent
	 */

	public BodyContent pushBody() {
		return null; // XXX to implement
	}

	/**
	 * Provides convenient access to error information.
	 *
	 * @return an ErrorData instance containing information about the
	 * error, as obtained from the request attributes, as per the
	 * Servlet specification.  If this is not an error page (that is,
	 * if the isErrorPage attribute of the page directive is not set
	 * to "true"), the information is meaningless.
	 * @since 2.0
	 */
	public ErrorData getErrorData() {
		int status = 0;

		Integer status_code = (Integer) getRequest().getAttribute(
				RequestDispatcher.ERROR_STATUS_CODE);
		// Avoid NPE if attribute is not set
		if (status_code != null) {
			status = status_code.intValue();
		}

		return new ErrorData(
				(Throwable) getRequest().getAttribute(
						RequestDispatcher.ERROR_EXCEPTION),
				status,
				(String) getRequest().getAttribute(
						RequestDispatcher.ERROR_REQUEST_URI),
				(String) getRequest().getAttribute(
						RequestDispatcher.ERROR_SERVLET_NAME)
		);
	}

}
